The invention relates to a sheet-fed rotary printing press having at least one unit which includes an impression cylinder and an additional cylinder assigned to the impression cylinder, the impression cylinder and the additional cylinder being relatively adjustable a spaced distance from one another.
In multicolor sheet-fed rotary printing presses, downline from which a varnishing unit is disposed, the transported sheets are printed with ink only in the initial printing units during the printing operation. Downline printing and varnishing units, respectively, are in an idling mode wherein the rubber blanket cylinder and the varnish blanket cylinder, respectively, are disengaged from the printing cylinder. A small gap is formed therebetween, through which the previously printed sheets are transported. Because of the high press speed, the sheets lift away from the respective printing cylinder, so that the freshly applied ink comes into contact with the rubber blanket or varnish blanket and smears.
The published German Patent Document DE 43 18 777 C2 shows a printing unit of a sheet-fed rotary printing press, wherein devices for aiding or promoting sheet guidance are provided, in order to avoid, respectively, smearing of and damage to the freshly printed image. The provisions taken in the heretofore known devices, however, are not always effective because, for example, in a rear region of the sheet, contact of the sheet end with the rubber blanket or the varnish blanket cylinder occurs, nevertheless, when the printing is performed on stiff sheet material.
In view of the aforementioned prior art, it is an object of the invention of the instant application to provide a sheet-fed rotary printing press which enables smear-free sheet travel when the printing, varnishing or finishing units are shut down.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a sheet-fed rotary printing press having at least one unit including an impression cylinder and an additional cylinder assigned to the impression cylinder, the impression cylinder and the additional cylinder being relatively adjustable a spaced distance from one another, a sheet guiding device disposed on the additional cylinder for keeping sheets of printing material, which have been transported by the impression cylinder past the additional cylinder, away from the additional cylinder, once the spaced distance between the impression cylinder and the additional cylinder has been set.
In accordance with another feature of the invention, the additional cylinder is stoppable, so that it will not rotate while the impression cylinder rotates.
In accordance with a further feature of the invention, the sheet-fed rotary printing press includes a clutch via which the additional cylinder is decouplable from a printing-press drive for driving the additional cylinder.
In accordance with an added feature of the invention, the additional cylinder is formed with a cylinder gap approximately alignable with the impression cylinder in a stopped condition of the additional cylinder, for setting the spaced distance between the additional cylinder and the impression cylinder.
In accordance with an additional feature of the invention, the sheet-fed rotary printing press includes a detent for fixing the additional cylinder relative to a printing-press frame, in a position of the additional cylinder wherein the cylinder gap formed therein is in alignment with the impression cylinder, and in a condition wherein the additional cylinder is decoupled from a printing-press drive for driving the additional cylinder.
In accordance with an alternative feature of the invention, the sheet-fed rotary printing press includes a blast air connection for fixing the additional cylinder relative to a printing-press frame, in a position of the additional cylinder wherein the cylinder gap formed therein is in alignment with the impression cylinder, and in a condition wherein the additional cylinder is decoupled from a printing-press drive for driving the additional cylinder.
In accordance with yet another feature of the invention, the sheet guiding device includes at least one sheet guiding element secured to the additional cylinder.
In accordance with another feature of the invention, the additional cylinder has a displaceable outer portion; and the sheet guiding element is disposed at the displaceable outer portion. In particular, the sheet guiding element may be embodied as a surface of the displaceable outer portion.
In accordance with yet another feature of the invention, the additional cylinder is stoppable in a position wherein the displaceable outer portion thereof is disposed opposite the impression cylinder.
In accordance with yet another feature of the invention, the displaceable outer portion of the additional cylinder has a clamping device for a cylinder covering to be mounted on the additional cylinder.
In accordance with another feature of the invention, the displaceable outer portion of the additional cylinder forms part of a circular outer surface of the additional cylinder.
In accordance with yet a further feature of the invention, the displaceable outer portion of the additional cylinder is removably fastened to the additional cylinder.
In accordance with yet another feature of the invention, the displaceable outer portion of the additional cylinder is displaceable into an interior of the additional cylinder.
In accordance with another feature of the invention, the displaceable outer portion of the additional cylinder is mounted so as to be pivotable about an axis aligned parallel to an axis of rotation of the additional cylinder.
In accordance with yet another feature of the invention, the sheet guiding element is an outwardly pivotable sheet guiding element.
In accordance with a further feature of the invention, the sheet guiding element is formed with a surface which, when in an outwardly displaced position, extends concentrically with a surface of the impression cylinder.
In accordance with yet another feature of the invention, the displaceable outer portion of the additional cylinder is displaceable linearly in a direction towards the interior of the additional cylinder.
In accordance with yet a further feature of the invention, the sheet guiding element is formed as at least one guide tongue.
In accordance with an alternative feature of the invention, the sheet guiding element is formed as at least one small wheel.
In accordance with another alternative feature of the invention, the sheet guiding element is formed as at least one blast tube.
In accordance with yet a further feature of the invention, the blast tube is couplable to a blast air connection at an end face of the additional cylinder.
In accordance with yet an added feature of the invention, the additional cylinder is formed with a cylinder gap, and the sheet guiding element being received in the cylinder gap.
In accordance with yet an additional feature of the invention, at least one cylinder of the impression cylinder and the additional cylinder is constructed so as to be engageable with and disengageable from the other for setting the spaced distance between the impression cylinder and the additional cylinder.
In accordance with still another feature of the invention, the sheet-fed rotary printing press includes a cylinder covering or liner on the additional cylinder, the cylinder covering being removable from the additional cylinder for setting the spaced distance between the impression cylinder and the additional cylinder.
In accordance with still a further feature of the invention, the impression cylinder and the additional cylinder, between which the spaced distance is set, are rotatable in common with one another, while the sheet guiding device acts upon the sheet to be printed.
In accordance with still an added feature of the invention, the sheet guiding device includes blast air nozzles disposed on the circumferential surface of the additional cylinder.
In accordance with still an additional feature of the invention, the additional cylinder has a stationary cylinder core formed with a chamber chargeable with blast air, and an outer casing rotatable about the stationary cylinder core, the outer casing having blast air ducts leading to the blast air nozzles.
In accordance with another feature of the invention, the sheet-fed rotary printing press includes a rotary valve assigned to the additional cylinder and, upon rotation of the additional cylinder, intermittently subjecting the rotating blast air nozzles to blast air whenever the blast air nozzles are directed generally towards the impression cylinder.
In accordance with a further feature of the invention, the at least one unit is a printing unit, and the additional cylinder is a cylinder for printing on the sheet to be printed.
In accordance with an alternative feature of the invention, the at least one unit is a varnishing unit, and the additional cylinder is a cylinder for varnishing the sheet to be printed.
In accordance with another alternative feature of the invention, the at least one unit is a finishing unit, and the additional cylinder is a processing cylinder having a circumference occupied by tools for processing the sheet to be printed.
In accordance with a concomitant feature of the invention, the at least one unit is disposed downline from at least one printing unit of the sheet-fed rotary printing press, as viewed in a sheet transport direction therethrough.
Preferably, the sheet guiding device forces the sheet to be printed approximately in the direction of the impression cylinder.
In accordance with another feature of the invention, a first electric motor is drive-connected to the impression cylinder for rotating the impression cylinder; and a second electric motor is drive-connected to the additional cylinder for rotating the additional cylinder.
In accordance with yet another feature of the invention, an electronic control device is connected to the first and second electrical motors; and the electronic control device controls the first electric motor such that the first electric motor rotates the impression cylinder with a first circumferential surface speed, and the electronic control device controls the second electric motor such that the second electric motor simultaneously rotates the additional cylinder with a second circumferential surface speed equal to the first circumferential surface speed.
In accordance with a further feature of the invention, a current circuit including an integrated breaker for interrupting the current circuit is provided; and the additional cylinder and the impression cylinder is controlled such that, when the breaker interrupts the current circuit, the additional cylinder is shut down and stopped while the impression cylinder rotates.
Preferred embodiments of the invention are based on the realization that it is markedly simpler to avoid smearing if the nip between the first cylinder, i.e., the impression cylinder, and the second cylinder, i.e., the rubber blanket or varnishing blanket cylinder, for example, that is associated therewith, is enlarged or widened beyond the extent that is predefined when the cylinders are disengaged or brought out of contact. This is preferably performed by stopping the second cylinder, i.e., the rubber blanket or varnishing blanket cylinder, and, if necessary, after removing the rubber blanket or varnishing blanket, displacing a segment or portion of the cylinder. This displacement may be performed by removing the relevant portion and the relevant segment of the cylinder, respectively, i.e., disassembled or simply displaced into the interior of the cylinder, which is particularly expedient. This can be effected by appropriately rotating the aforementioned segment and portion of the cylinder, respectively, or by a linear movement which displaces the segment away from the impression cylinder into the interior of the rubber blanket and varnishing blanket cylinder, respectively. During subsequent printing, this further rubber blanket and varnishing blanket cylinder, respectively, remains uncoupled from the drive of the printing machine, for example, by a clutch, in a position wherein the removed or displaced segment is located opposite the impression cylinder. In this way, the distance between the impression cylinder, on the one hand, and the rubber blanket and varnishing blanket cylinder, respectively, on the other hand, can be enlarged or widened to such an extent that the risk of smearing is reduced considerably or is largely avoided, depending upon the printing speed and the stiffness of the printing material.
It is advantageous if, for this purpose, the clamping device or devices needed for clamping the rubber and varnishing blanket, respectively, in the cylinder gap of the relevant cylinder are displaced, these installed cylinder-gap fittings either being removed or, what is particularly expedient, being pivoted into the interior of the cylinder about an axis parallel to the cylinder axis. This is because the latter measure can be performed rapidly and simply, when provided with a suitable design, and, if necessary, can also be automated.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a sheet-fed rotary printing press, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.